Temperature control of an optical device

ABSTRACT

The present disclosure is directed to an optical device including at least one temperature-dependent tunable element for controlling a wavelength of an optical signal, a first temperature control circuit for controlling a temperature of a first region of the optical device; and a second temperature control circuit for controlling a temperature of a second region of the optical device. The second region may include a portion of the first region. The second region may be smaller than the first region. The tunable element may be positioned in the second region such that a temperature of the tunable element is controlled based on the second temperature control circuit controlling the temperature of the second region. The tunable element may be one of (i) a laser for transmitting an outgoing optical signal and (ii) an optical filter coupled to a photodetector for receiving an incoming optical signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 15/978,295 filed May 14, 2018, which claims the benefit of thefiling date of U.S. Provisional Patent Application No. 62/507,279 filedMay 17, 2017, U.S. Provisional Patent Application No. 62/507,283 filedMay 17, 2017, and U.S. Provisional Patent Application No. 62/635,207filed Feb. 26, 2018, the disclosures of which are hereby incorporatedherein by reference

BACKGROUND OF THE INVENTION

In optical transmission systems, cables, such as fiber-optic cables, areused to transmit information. In some systems, the cables extend from anoptical line terminal (“OLT”) or other optical device to one or moreoptical network units (“ONUs”). Optical signals of a certain group ofwavelengths are transmitted (upstream signal) from the optical device tothe ONUs. Additionally, optical signals of a certain group ofwavelengths, which may be different from the group of wavelengths of thetransmitted optical signals, are received (downstream signal) from theONUs at the optical device.

In order for the optical device to transmit or receive at a desiredwavelength from among the group of wavelengths, the device must betuned. For an upstream signal, the signal generator (e.g., laser) of thedevice may be tunable to provide what is effectively a “pre-filtered”signal. Alternatively, the laser may transmit an optical signal to adestination ONU with an optical transmission made up of multiplewavelengths (with minimal or no filtering applied), and the opticalsignal can be filtered from the transmission at the destination ONU.Similarly, the ONU may transmit a multiple-wavelength optical signal tothe optical device, and the signal can be filtered at the opticaldevice. In order to filter such a signal, a tunable optical filter maybe provided. To accommodate for transmitting and receiving both“pre-filtered” and non-“pre-filtered” optical signals, the opticaldevice may include either or both of a laser and optical filter that canbe tuned to a frequency that corresponds to the desired wavelength.Conventionally, this tuning is performed by changing the temperature ofthe laser/optical filter. Thus, tuning at the optical device may beperformed using a temperature dependent tunable element.

As passive optical networks (PONs) become increasingly faster, itbecomes increasingly more important for the tunable element to be tunedat a high speed. At the same time, while it is important to be able totune the tunable element at a high speed, it is also necessary for thetuning to be precise and accurate in order to minimize attenuation ofthe desired downstream or upstream signal (e.g., as it passes throughthe cable or filter). In other words, it is desirable to both rapidlyand precisely change a temperature of the tunable element. It is furtherdesirable for the optical device to have a relatively compact size, andto minimize the cost of the temperature control components, as well asthe cost of their installation.

It is generally known that a thermoelectric cooler (TEC) may be used tostabilize the temperature of an optical device in order to stabilize thewavelength of the upstream or filtered downstream optical signal.However, the TEC changes the temperature of the device at a relativelyslow rate. The TEC would need to be able to change the temperature ofthe tunable element at a faster rate in order to be a suitable tuningmechanism.

In the case of a laser that is operated in burst-mode, it is alsogenerally known that a heater may be used to stabilize the temperatureof the laser, thereby stabilizing the wavelength of the light emittedfrom the laser. Without temperature stabilization achieved by theheater, the wavelength of light emitted from the laser could drift dueto temperature fluctuations in the laser caused by the abrupttransitions between on (emitting light) and off (not emitting light)modes. Generally, the heater is used to keep the laser warm while it isoff so that there is no temperature fluctuation when the laser is turnedon. However, operating the heater in an efficient manner is challenging.It is only necessary for the laser to be kept warm just before it isturned on; therefore, it is not necessary to operate the heater theentire time the laser is off. But because of the unpredictable nature ofstatus transitions when operating the laser in burst-mode, it is notknown when the laser will turn on. Additionally, the amount of time forwhich the laser is off varies from cycle to cycle, making the amount oftime and energy needed to warm the laser inconsistent as well.

BRIEF SUMMARY OF THE INVENTION

The present disclosure is directed to various embodiments of opticaldevices, optical control systems, and methods that provide for fast,accurate and stable tuning of an optical signal. This is accomplished byproviding at least two temperature control devices in the opticaldevice. A first temperature control device may be used to maintain theoverall temperature of the device within a temperature range over whichthe device may reasonably operate. A second temperature control devicemay be used to control the temperature of a focused region of theoptical device, the focused region including the tunable element.Because the second temperature device is confined to the focused region,it is able to change the temperature of the focused region much morequickly than the first temperature control device can change the overalltemperature of the device. In this manner, the first temperature controldevice provides coarse temperature control over a relatively wide rangeof temperatures across a relatively wide space, whereas the secondtemperature control device provides fine temperature control over arelatively narrower range of temperatures in a relatively narrow space.

The first and second temperature control devices may also be thought ofas providing dual stage temperature control, with the first temperaturecontrol device being responsible for keeping the device “close” to thedesired temperature of the tunable element, and the second temperaturecontrol device being responsible for adjusting the precise temperatureof the tunable element in order to facilitate operation of the opticaldevice (and reduce attenuation of the optical signal).

In the case of a laser operating in burst-mode, a time delay can beimplemented between a burst-mode switch signal and the laser turning onin order to provide sufficient time to heat the laser to or close to itsnormal operating temperature. During the delay, a third temperaturecontrol device may be used to heat the laser. The magnitude and durationof the electric current provided by the temperature control device toheat the laser may vary from cycle to cycle, depending on the previouson and off times of the burst-mode switch signal. Stated another way,the third temperature control device may be thought of as a heater, andthe temperature of the heater and how long it is kept on may vary as afunction of how long the laser was previously off.

One aspect of the present disclosure is directed to an optical deviceincluding at least one temperature-dependent tunable element forcontrolling a wavelength of an optical signal, a first temperaturecontrol circuit for controlling a temperature of a first region of theoptical device, and a second temperature control circuit for controllinga temperature of a second region of the optical device. The tunableelement may be one of (i) a laser for transmitting an outgoing opticalsignal and (ii) an optical filter coupled to a photodetector forreceiving an incoming optical signal. The second region may include aportion of the first region. The second region may be smaller than thefirst region. The tunable element may be positioned in the second regionsuch that a temperature of the tunable element is controlled based onthe second temperature control circuit controlling the temperature ofthe second region.

In some examples, at least one of the first and second temperaturecontrol circuits may be a thermoelectric cooler, or a thin film heater.The second temperature control circuit may be configured to control thetemperature of the tunable element across a range of at least 24° C.

For those devices that include a laser, the laser may be configured totransmit an optical signal at any of at least four differentwavelengths, and the wavelength of the optical signal transmitted by thelaser may be based on the temperature of the laser. In some examples,the device may be an optical transceiver, meaning that it includes eachof the laser, the photodetector, and the optical filter. Opticaltransceivers may be configured to perform one of wavelength-divisionmultiplexing (WDM), dense wavelength-division multiplexing (DWDM), andcoarse wavelength-division multiplexing (CWDM), or other kinds of WDM.

In some examples, the second region may be defined by a housing, and thesecond temperature control circuit may be configured to control thetemperature inside the housing. If the first temperature control deviceis communicatively coupled to the second temperature control device, itmay be operable to provide an indication of the temperature of the firstregion to the second temperature control device. The second temperaturecontrol device may then be configured to control the temperature of thesecond region based on the indication of the temperature of the firstregion.

In some examples, the optical device may further include a controlcircuit configured to receive an indication of an ambient temperature atthe optical device's location, and to control the respectivetemperatures of the first and second regions with respect to each otherbased on the indication of the ambient temperature.

In some examples, the second temperature control device may beconfigured to heat the tunable element. In such examples, the firsttemperature control device may be configured to maintain the firstregion at a temperature lower than the second temperature control devicemaintains the second region, whereby when the second temperature controldevice is off, the tunable element may be cooled, and when the secondtemperature control device is on, the tunable element may be heated.Additionally or alternatively, the second temperature device may beconfigured to adjust the temperature of the second region at a fasterrate than the first temperature device is configured to adjust thetemperature of the first region.

Another aspect of the present disclosure is directed to a controlsystem, such as a controller or control circuit, included in a devicehaving at least one of (i) a tunable optical transmitter configured toselectively generate a first optical signal at one of a plurality ofpreselected wavelengths or (ii) an optical receiver coupled to a tunableoptical bandpass filter configured to selectively pass a second opticalsignal at one of a plurality of preselected wavelengths. The controlsystem may be configured to receive one or more temperature-indicativemeasurements from one or more corresponding sensors, transmit a firstcontrol signal to a first temperature control circuit to control atemperature of the device based on one of the receivedtemperature-indicative measurements, and transmit a second controlsignal to a second temperature control circuit to control a temperatureof the tunable optical transmitter or the tunable optical bandpassfilter based on one of the received temperature-indicative measurements.

In some examples, the control system may include a first control circuitcoupled to a first sensor that senses an ambient temperature at alocation of the device, and a second control circuit coupled to a secondsensor that senses a property indicative of a temperature of the tunableoptical transmitter or the tunable optical bandpass filter. The firstcontrol signal may be based on a first temperature measurement of thefirst temperature sensor, and the second control signal may be based onthe property sensed by the second sensor. If the control system iscoupled to a single sensor and to both the first and second temperaturecontrol circuits, it may be configured to provide the same controlsignal to both the first and second temperature control circuits basedon the measurement of the single sensor. In some instances, the secondcontrol signal may be based further on the first control signal. Also insome instances, the control system may be configured to control thetemperature of the tunable optical transmitter or the tunable opticalbandpass filter across a range of at least 24° C.

In some examples, the device may include each of the tunable opticaltransmitter, the optical receiver, and the optical bandpass filtercoupled to the receiver, and the second control signal may control thetemperature of the optical transmitter and the optical bandpass filterbased on at least one of the received temperature-indicativemeasurements.

Yet a further aspect of the present disclosure is directed to a methodfor controlling a device having at least one of (i) a tunable opticaltransmitter configured to selectively generate a first optical signal atone of a plurality of preselected wavelengths or (ii) an opticalreceiver coupled to a tunable optical bandpass filter configured toselectively pass a second optical signal at one of a plurality ofpreselected wavelengths. The method may involve: receiving one or moretemperature-indicative measurements from one or more correspondingsensors; transmitting a first control signal to a first temperaturecontrol circuit to control a temperature of the device based on one ofthe received temperature-indicative measurements; and transmitting asecond control signal to a second temperature control circuit to controla temperature of the tunable optical transmitter or the tunable opticalbandpass filter based on one of the received temperature-indicativemeasurements.

An even further aspect of the present disclosure is directed to each ofa control circuit and method for regulating a temperature of an opticaldevice that emits an optical signal at an operating wavelength, thetemperature of the optical device affecting the operating wavelength ofthe optical signal. The control circuit receives from a burst-modeswitch: a first signal indicating the burst-mode switch switching from afirst state to a second state, and a second signal indicating theburst-mode switch switching from the second state to the first state.The control circuit further controls a power source to provide electriccurrent to a heating element based on the first and second signalsbeginning at or after the control circuit receives the second signal andending at or after the second signal causes the optical device to emitan optical signal. The electrical current provided to the heatingelement causes the temperature of the optical device to increase. Theelectrical current provided to the heating element may reducefluctuations of the operating wavelength of the optical signal emittedby the optical device. In some instances, the optical device may beincluded in a time-division multiplexing passive optical network, andmay receive the first and second signals from the burst-mode switchwithin a 125 microsecond window.

In some examples, the system includes a current source configured togenerate the electric current provided to the heating element. Thecontrol circuit may be configured to control operation of the currentsource as a function of a time elapsed while the burst-mode switchsignal is in the second state. For instance, the control circuit may beconfigured to control a magnitude of the electric current provided tothe heating element as a function of a time elapsed while the burst-modeswitch signal is in the second state. For further instance, the controlcircuit may be configured to control a duration of the electric currentprovided to the heating element as a function of a time elapsed whilethe burst-mode switch signal is in the second state.

Yet a further aspect of the present disclosure is directed to a systemfor regulating a temperature of an optical device that emits an opticalsignal at an operating wavelength, the temperature of the optical deviceaffecting the operating wavelength of the optical signal. The system mayinclude a control unit and a time delay circuit. The control unit may beconfigured to receive a burst-mode switch signal for which switchingfrom a first state to a second state causes the optical device to stopemitting the optical signal, and switching from the second state to thefirst state causes the optical device to begin emitting the opticalsignal. The time delay circuit may create a time delay between (i) theburst-mode switch signal switching from the second state to the firststate and (ii) the optical device beginning to emit the optical signal.The control circuit may further be configured to determine an amount oftime that the optical device is not emitting the optical signal based onthe burst-mode switch signal, and control an electric current providedto the heating element for increasing the temperature of the opticaldevice. The control circuit may be configured to control the electriccurrent provided to the heating element only during the time delay.Increasing the temperature of the optical device may reduce fluctuationsin the operating wavelength of the optical signal.

In some examples, the time delay circuit may be communicatively coupledto the control circuit, whereby the control circuit provides theburst-mode switch signal to the delay circuit. Also, in some examples,the heating element may be included in a packaging of the opticaldevice, and the control circuit may be packaged separately from theheating element and coupled to the heating element by one or more wires.In some examples, the system may further include a burst-mode switchconfigured to provide the burst-mode switch signal.

In some examples, the power source may provide a non-zero electriccurrent to the heating element between the first and second signals, andthe control circuit may control the power source to increase the amountof current provided to the heating element based on the first and secondsignals. In some examples, the control circuit may control the powersource to provide electric current to the heating element as a functionof a time difference between the first and second signals. The controlcircuit may further control the power source to provide electric currentto the heating element according to the function, whereby the functionmay provide for at least one of a magnitude and a duration of theelectric current provided to the heating element to increase as the timedifference between the first and second signals increases. The controlcircuit may control the power source to provide electric current to theheating element according to the function, wherein the function providesfor zero electric current to be provided to the heating element when thetime difference is less than a threshold value. The threshold value maybe greater than the time between (i) the control circuit receiving thesecond signal and (ii) the second signal causing the optical device toemit an optical signal. In some examples, the time between (i) thecontrol circuit receiving the second signal and (ii) the second signalcausing the optical device to emit an optical signal may be a fixedamount of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an optical device in accordance with anaspect of the present disclosure.

FIG. 2 is a plot illustrating a temperature range of the optical deviceof FIG. 1.

FIG. 3 is a block diagram of another optical device in accordance withan aspect of the present disclosure.

FIG. 4 is a block diagram of a controller of an optical device inaccordance with an aspect of the present disclosure.

FIG. 5 is a flow diagram of a method in accordance with an aspect of thepresent disclosure.

FIGS. 6A, 6B and 6C are functional block diagrams of various examplecontrol systems in accordance with aspects of the present disclosure.

FIG. 7 is a block diagram of yet another optical device in accordancewith an aspect of the present disclosure.

FIG. 8 is a block diagram of a further optical device in accordance withan aspect of the present disclosure.

FIG. 9A is a plot illustrating a signal pattern of a burst-mode switchover time in accordance with an aspect of the present disclosure.

FIG. 9B is a plot illustrating a signal pattern of a laser emitting anoptical signal over time in accordance with an aspect of the presentdisclosure.

FIG. 9C is a plot illustrating current output of a temperature controlunit over time in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of an optical device 100 for receiving anoptical signal at an optical signal receiver 106, such as aphotodetector, from one or more optical network units over a cable 105,such as an optical fiber. The optical fiber may be, but is not limitedto being made of glass fibers.

The optical signal is filtered by a tunable optical filter 108. Theoptical filter 108 may be a partially transmitting and partiallyreflecting optical filter, commonly known as a TAP filter. The opticalfilter may be, but is not limited to being, made of any one of glass,plastics such as polycarbonates or acrylics, or a multilayered thin filmcoating made of dielectric materials, such as SiO₂ and TiO₂. The opticalfilter 108 may be temperature-dependent, meaning that the temperature ofthe filter affects its operation. For example, if the filter is abandpass filter, then the central wavelength passed by the filter mayshift as the temperature of the filter changes. The correlation betweenfilter temperature and central wavelength may be predefined based on theproperties of the filter.

The optical device 100 further includes two temperature control devices.The temperature control devices may be, but are not limited to being,thermoelectric coolers or thin film heaters. One or both of thetemperature control devices may be externally installed or embedded inthe optical device. In some cases, one or both of the temperaturecontrol devices may be co-fabricated with the optical device, generallywhen the temperature control device is implemented for heating purposesonly.

A first temperature control device 122 is positioned to providetemperature control of a first region 112 of the optical device 100. Inthe example of FIG. 1, the first region is defined by a first regionboundary 102. In some instances, the first region 112 may be the portionof the optical device 100 that is housed inside of a casing, such thatin FIG. 1 the casing is represented by the first region boundary 102. Inother instances, the first region 102 may be a subset of a space withinthe casing of the optical device 100. In either case, the firsttemperature control device 122 may be positioned within the first region112 or on the first region boundary 102.

A second temperature control device 124 is positioned to providetemperature control of a second region 114 of the optical device 100.The second region 114 may include a portion of the first region 112,such that the two regions at least partially overlap. The second region114 may also be smaller than the first region 102, such that the secondtemperature control device 124 is responsible for cooling less spacethan is the first temperature control device 122. In the particularexample of FIG. 1, the second region 114 is a subset of the first region112. As with the first region 112, FIG. 1 illustrates the boundary ofthe second region 114 using by way of a second region boundary 104.Importantly, the optical filter 108 is positioned in the second region114, such that controlling the temperature of the second region 114 alsocontrols the temperature of the optical filter 108.

In some instances, the second region boundary 104 may include the spacewithin a given radius of the second temperature control device 124.Thus, placing the second temperature control device 124 in closeproximity (e.g., within said radius) to the optical filter ensures thatthe second temperature control device 124 may rapidly and accuratelycontrol the temperature of the filter 108 without having to affect thetemperature of the entire first region 102 of the device 100. If thesecond temperature control device 124 is a TEC, then the second region114 may further be defined by an orientation of the TEC, such that thesecond region extends in a direction in which the TEC faces.

Additionally or alternatively, the second region may be defined by acasing or housing that fully or partially encloses the optical filter108. Such a casing may be useful for confining the effect of secondtemperature control device 124. Thus, placing the second temperaturecontrol device 124 on or within the casing also ensures that the secondtemperature control device 124 may rapidly and accurately control thetemperature of the filter 108 without having to affect the temperatureof the entire first region 102 of the device 100. In such instances, thecasing may be represented by the second region boundary 104 of FIG. 1.

In the specific example of FIG. 1, the optical filter 108 is integratedwith the photodetector 106 in a common housing, and a TEC 124 (providedas the second temperature control device) is positioned on or in closeproximity to the common housing of the photodetector 106/optical filter108. In this manner, the TEC 124 is responsible only for controlling thetemperature of the photodetector (and the integrated filter), and notfor controlling the overall temperature of the optical device 100.

Because the second temperature control device 124 is needed only forregulating temperature of the filter 108, the temperature range of thesecond temperature control device 124 may be relatively narrow comparedto the temperature range of the first temperature control device 122.For instance, the optical device 100 may be configured to receiveoptical signals at any one of “n” predetermined channels, and theoptical filter 108 may be configured such that a temperature changecauses the center wavelength passed by the filter to shift about “x” nmper degree Celsius. Then, for a desired spacing of “y” nm betweenchannels, it is necessary to control the temperature of the opticalfilter 108 across a range of

$\left\lbrack {\left( {n - 1} \right) \cdot \frac{y}{x}} \right\rbrack\mspace{14mu}{^\circ}\mspace{14mu}{C.}$

In other instances, the control range of the second temperature controldevice 124 may be wider than that of the first temperature controldevice 122. Furthermore, the two temperature ranges may, but do notnecessarily, overlap with one another. For instance, if the firsttemperature control device 122 is capable of heating and cooling, andthe second temperature control device 124 is capable of heating only,then the first temperature control device 122 may heat and cool theoverall device within a relatively narrow range of operationaltemperatures, and the second temperature control device 124 may heat theoptical filter over a wider range of temperatures, all of which may behotter than the suitable range of temperatures of the overall device. Insuch an instance, the first temperature control device 122 may be usedto create a local heat sinking region at a relatively low temperature(e.g., if the ambient temperature is high) so that when the secondtemperature control device 124 is off, the optical filter 108 of thedevice 100 cools relatively fast due to a large temperature gradientwithin the device 100. Conversely, when the second temperature controldevice 124 is on, the optical filter 108 is heated relatively fast dueto the heating of the second temperature control device 124.

For example, if a device receives optical signals at any one of fourchannels using wavelength division multiplexing (WDM) technologyrequiring 100 GHz (about 0.8 nm) spacing in optical frequency betweenchannels, and if a temperature change causes the optical filter to shift0.1 nm/° C., then the required temperature range of the secondtemperature control device 124 is about

${\left( {4 - 1} \right) \cdot \frac{0.8}{0.1}} = {24{^\circ}\mspace{14mu}{C.}}$For further example, if the device uses dense wavelength divisionmultiplexing (DWDM) technology requiring 50 GHz (about 0.4 nm) spacingin optical frequency between channels, then the required temperaturerange of the second temperature control device 124 would be about

${\left( {4 - 1} \right) \cdot \frac{0.4}{0.1}} = {12{^\circ}\mspace{14mu}{C.}}$

By contrast, the first temperature control device 122 is needed forregulating the overall temperature of the optical device 100 andisolating that temperature from its surrounding environment. The overalltemperature of the optical device may be influenced by the ambienttemperature of the device's surroundings, and the ambient temperaturecan vary by much more than 24° C. Keeping the temperature of the entireoptical device 100 within the 24° C. range of operation of the filter108 may require a significant amount of power. Instead, it is moreefficient (both in terms of cost and energy) for the first temperaturecontrol device 122 to merely isolate the temperature of the entireoptical device 100 from its environment, keeping it close to but not atthe operational range of the optical filter 108. The presence of thefirst temperature control device 122 reduces the amount of power neededfor the second temperature control device 124 to keep the temperature ofthe optical filter 108 within its operational range. The presence of thefirst temperature control device 122 also reduces the temperaturegradient between the first region 112 and second region 114 of theoptical device 100, thereby improving the second temperature controldevice's ability to rapidly control the temperature in the second region112.

Altogether, the operational temperature range of the second temperaturecontrol device may be relatively narrow compared to the operationaltemperature range of the first temperature control device. By way ofexample, FIG. 2 illustrates an example in which the relative temperatureranges of first and second temperature control devices, such as thoseshown in FIG. 1, and in which the range of the second temperaturecontrol device is subsumed within the range of the first temperaturecontrol device. As shown in FIG. 2, the temperature range of the firsttemperature control device 122 is from T₁ to T₄, whereas the temperaturerange of the second temperature control device 124 is from T₂ to T₃, forwhich T₁<T₂<T₃<T₄.

Many optical devices are designed to operate within a range oftemperatures from −40° C. to 85° C. The temperature range between T₁ andT₄ may extend across the full range of operational temperatures, but inmany cases may be limited due to factors such as power consumption,thermal mechanical design, and temperature control devicespecifications. In one example optical device, the temperature rangebetween T₂ and T₃ may be about 24° C. or 25° C. Such a temperature rangemay be suitable for a second temperature control device even when thesecond temperature control device performs heating only, and thetemperature range of the first temperature control device is narrowerand does not overlap with that of the second temperature control device.

FIG. 2 also illustrates four predetermined wavelengths λ₁, λ₂, λ₃ and λ₄or channels at which the optical device photodetector is configured toreceive an optical signal. These wavelengths are plotted against therange of temperatures since there is a one-to-one relationship between agiven temperature and the wavelength passed by the filter at thattemperature. The second temperature control device 124 is configured toselectively adjust the temperature of the filter to any one of thetemperatures corresponding to the predetermined wavelengths λ₁, λ₂, λ₃and λ₄. Therefore, temperatures T₂ and T₃ must be selected such thateach of the predetermined wavelengths necessarily corresponds to atemperature between T₂ and T₃ (T₂<T(λ₁)<T(λ₂)<T(λ₃)<T(λ₄)<T₃).

In the example of FIG. 2, the predetermined wavelengths are equallyspaced. However, in examples involving other optical devices, thepredetermined wavelengths may be spaced unevenly, provided that thewavelengths are spaced apart by at least a threshold minimum.

The example of FIG. 1 illustrates an optical device with a temperaturedependent receiver. However, the same concepts may apply to atemperature dependent transmitter. For example, FIG. 3 is a blockdiagram of another optical device 300 for generating and transmitting anoptical signal from an optical signal generator 306 or transmitter, suchas a laser, to one to or more optical network units over a cable 305,such as an optical fiber. As in FIG. 1, the optical fiber of FIG. 3 maybe, but is not limited to being, made of glass fibers.

The optical signal generator 306 may be temperature-dependent, meaningthat its temperature affects its operation. For example, in the case ofa laser, the temperature of the laser affects the wavelength of lightoutputted by the laser. The correlation between laser temperature andwavelength may be predefined based on the properties of the laser.

The optical device 300 of FIG. 3 includes two temperature controldevices, which may be compared to the above-described temperaturecontrol devices of FIG. 1. The first temperature control device 322 ispositioned so as to control the temperature of a first region 312defined in FIG. 3 by boundary 302. The second temperature control device324 is positioned so as to control the temperature of the second region314 defined in FIG. 3 by boundary 304. The first and second boundariesmay be physical boundaries of the device 300 (e.g., a housing of thedevice 300, a casing at least partially surrounding the laser 306, etc.)non-physical boundaries representative of the space controlled by therespective temperature control devices. As described above, the secondregion 314 may partially overlap with the first region 312 or may besubsumed within the first region 312. The second region 314 may also besmaller than the first region 312. Additionally, in order to causerelatively fast temperature control of the optical signal generator 306,the optical signal generator is positioned in the second region 314.

Similar to the filter described above in connection with FIGS. 1 and 2,the optical signal generator 306 may be configured to emit an opticalsignal at one of any plurality of predetermined wavelengths (e.g., 4wavelengths). Each of those wavelengths may correspond to a predefinedtemperature, and the second temperature control device 324 may beconfigured to adjust the temperature of the optical signal generator 306to correspond with a desired output wavelength. Thus, the secondtemperature control device 324 may be configured to control thetemperature of the optical signal generator 324 within a range oftemperatures that includes the temperatures corresponding to each of theplurality of predetermined wavelengths. This range of temperatures maybe narrower than the operational range of the first temperature controldevice 322.

The temperature control devices described above may be operated usingone or more controllers. The one or more controllers may be integratedwith one or both of the temperature control devices. Additionally oralternatively, the controller(s) may be integrated with the opticaldevice apart from the temperature control devices. Additionally oralternatively, the controller(s) may be standalone devicescommunicatively coupled to the optical device and temperature controldevices.

FIG. 4 is a block diagram of an example controller 400. Thecontroller(s) may include one or more processors 410 (e.g., centralprocessing units, application-specific integrated circuits, fieldprogrammable gate arrays, etc.), memory 420 (e.g., hard-drive, ROM, RAM,CD-ROM, write-capable, read-only, etc.) storing both data 430 andinstructions 440, an input interface 450 for receiving data, and anoutput interface 460 for transmitting instructions and optionally data.

While one processor block is shown, the controller 400 may also includemultiple processors which may or may not operate in parallel. Theprocessor 410 may carry out programmed instructions stored in the memory420.

The stored data 430 may include temperature measurements, such as anambient temperature of the device's surroundings 432, or a temperatureof the temperature-dependent tunable element of the device 434 (e.g., anoptical filter, an optical signal generator). The temperaturemeasurements may be received by the controller via the input interface.In some instances, the temperature measurements may be collected fromone or more temperature sensors 470 coupled to the controller 400. Forinstance, the one or more sensors may include a temperature sensorconfigured to sense a temperature of the optical filter. The temperaturesensor may be, but is not limited to being, a resistive temperaturesensor such as Negative Temperature Coefficient (NTC) thermistor orPositive Temperature Coefficient (PTC) thermistor. In such instances,the controller 400 may receive a measurement of the temperature 434 fromthe temperature sensor.

Alternatively, the temperature of the tunable element may be determinedusing the wavelength of the optical signal. For example, the wavelengthof light passed through an optical filter may be indicative of thefilter's temperature. Similarly, the wavelength of light generated by alaser may be indicative of the laser's temperature. In such instances,the controller 400 may receive a measurement of the passed/generatedwavelength 436, and determine the tunable element's temperature based onthe received measurement. The wavelength measurement may be receivedfrom a wavelength meter or spectrum analyzer at the input interface ofthe controller.

The stored data may further include correlation information 438 (such asa data table) correlating given optical signal wavelengths withcorresponding temperatures for the tunable element in order to properlyset the temperature control devices to the appropriate temperaturescorresponding to a desired wavelength. In the case of an optical deviceincluding a wavelength sensor, the correlation information may also beused to correspond the wavelength measurements to temperature in orderto measure temperature based on wavelength.

Alternatively or additionally, in the case of a tunable optical filter,the wavelength passed through the filter may be measured using aphotodetector connected to an output end of the filter. Since it isknown that the downstream optical signal received is to be received atone of four predetermined wavelengths, if the optical filter is centeredclose to but not at one of those predetermined wavelengths, thedeviations in the center wavelength of the filter may result inattenuation of the received optical signal. The photodetector may detectthis attenuation if the magnitude of the optical signal is below apreset threshold, or drops by a predetermined threshold amount. Thus,current measurements of the photodetector could be used to monitor thecenter wavelength of the filter, and the controller could instruct thesecond temperature control device to adjust the filter temperature tocorrect the sensed deviation in central wavelength. Optical deviceshaving a temperature control based on current measurement are describedin greater detail in the commonly owned priority application Ser. No.62/507,283, the disclosure of which is hereby incorporated in itsentirety herein.

Sensors 470 (e.g., temperature sensors, wavelength sensors,photodetectors) are not shown in FIGS. 1 and 3, but it will beunderstood that they may be placed anywhere within or around the devicesuch that they are capable of collecting the above specifiedmeasurements.

Using the one or more processors, the controller(s) may analyze 442 thereceived temperature data and determine a desired temperature for eachof the first and second temperature control devices based on theanalysis. The determined temperatures are then communicated to thetemperature control devices via the output interface 460.

FIG. 5 is a flow diagram illustrating an example routine 500 by which acontroller may perform the above described operations. It should beunderstood that the operations of the example routine 500 do not have tobe performed in the precise order described below. Rather, variousoperations can be handled in a different order, or simultaneously.Moreover, operations may be added or omitted.

At 502, the controller receives one or more temperature-indicativemeasurements from the sensors. As noted above, a temperature-indicativemeasurement may be direct measurements of temperature, or othermeasurements that are indicative of temperature (e.g., wavelength). Inthe same manner, the sensors may sense either temperature or otherinformation that is indicative of temperature (e.g., wavelength). Insome instances, the controller(s) may receive more than one temperaturemeasurement.

At 504, the controller determines a desired temperature of the opticaldevice based on one or more of the received measurements. Thistemperature may be based on an ambient temperature of the device'ssurroundings, and may be chosen to effectively isolate,temperature-wise, the device from its surroundings.

At 506, the controller determines a desired temperature of the tunableelement (e.g., filter, laser) based on one or more of the receivedmeasurements. The desired temperature may be determined based on acorrelation with a selected wavelength or channel of the tunable element(e.g., selected by a user), which may be received by the controller(s)via the input interface. In other words, the controller may determinethe temperature of the tunable element required for the optical deviceto operate at the selected channel.

At 508, the controller transmits a first control signal to a firsttemperature control device via the output interface. The first controlsignal may instruct the first temperature control device to control,maintain or otherwise regulate the temperature of the device.

At 510, the controller transmits a second control signal to a secondtemperature control device via the output interface. The second controlsignal may instruct the second temperature control device to control,maintain or otherwise regulate the temperature of the tunable element.

While FIG. 5 generally describes a routine executed by a singlecontroller, the same or similar routines may be executed using aplurality of controllers. For example, each of the first and secondtemperature control devices may be instructed by separate controllers.

FIG. 6A is a block diagram illustrating one example control scheme usingseparate controllers 612, 614 to control each of a first temperaturecontrol device (Device TEC 622) and a second temperature control device(Laser/Filter TEC 624). In the example of FIG. 6A, the first controller612 receives an input from an ambient temperature sensor 602, determinesa desired temperature of the device based on the input, and transmits aninstruction to the device TEC 622 based on the determination. The secondcontroller 614 receives an input from a tunable element (e.g., laser,filter) temperature sensor 604, and transmits an instruction to the TEC624 for the tunable element based on the determination. As explainedabove, the tunable element temperature sensor 604 may sense somethingindicative of temperature (e.g., wavelength) instead of temperatureitself in order to monitor operation of the tunable element.

It should be noted that the desired temperature of the tunable elementis based not on the element's temperature but rather on an instructionselecting a channel of the tunable element. Nonetheless, the controllermay use the temperature information in order to determine how to adjustthe TEC 624 to properly control the tunable element's temperature. Inother words, if the tunable element must be set to a wavelengthcorresponding to 15° C., it is necessary to know the current temperatureof the tunable element in order to know whether to heat the element,cool the element, or maintain it at its current temperature.

In alternative control schemes, at least one of the controllers mayreceive some or all of the information received by the other controller.FIG. 6B is a block diagram illustrating an example control scheme inwhich the second controller 614′ receives from the temperature sensor602′ the same ambient temperature information as the first controller612′, in addition to the tunable element temperature information 604′.The first and second controllers may then use the ambient temperatureinformation to coordinate the control scheme between the two TECs 622′and 624′. Coordinating the control scheme may allow for the controllersto optimize power use of the two TECs, thereby increasing efficiency andpotentially reducing cost).

FIG. 6C is a block diagram illustrating a similar scheme as in FIG. 6B,except that in FIG. 6C the second controller 614″ receives informationfrom both the first controller 612″ and the laser/filter temperaturesensor 604″. In this manner, the first controller may send instructionsto the second controller 614″, thereby coordinating with the secondcontroller 614″ more directly. In other words, the control scheme ofFIG. 6C utilizes a master/slave relationship between the twocontrollers. The master controller 612″ then controls the device TEC622″ based on information from the ambient temperature sensor 622″, andthe slave controller 614″ controls the laser/filter TEC 624″ based oneither or both of the master controller's instructions and thetemperature information from the laser/filter temperature sensor 604″.

In yet further configurations, one of the two controllers may receiveinformation from both sensors, and send instructions to the other of thetwo controllers. In yet further configurations, the two controllers mayreceive different information and then share the information over abidirectional communication connection. One or both of the controllersmay then determine instructions for controlling the TECs, and thoseinstructions may be relayed through the controllers to be transmitted tothe respective TECs.

The above example devices, methods, and control systems illustratetemperature control in an optical device that either sends or receivesoptical signals. However, it should be recognized that the sameprinciples may be applied to an optical transceiver that performs bothtransmitting and receiving optical signals. FIG. 7 is a block diagram ofan optical transceiver device 700 including a photodetector 706, a laser716 and a WDM 715 for controlling the transmission of optical signals toand from the photodetector and laser. The optical signals may betransmitted over cable 705 bi-directionally between the device 700 andone or more ONUs. The WDM may be any one of a coarse WDM, a dense WDM,or other WDM device for controlling a bidirectional stream of opticalsignals. The WDM is connected to the photodetector 706 via cable 709 andto the laser via cable 719, which, like cable 705, may be fiber opticalcables. Positioned between cable 709 and the photodetector 706 is anoptical filter 708. The laser, photodetector and optical filter may becomparable to the corresponding components described above in connectionwith FIGS. 1 and 3. Additionally, the optical signal channels of thephotodetector (e.g., λ₁, λ₂, λ₃ and λ₄) may be different from theoptical signal channels of the laser (e.g., λ₅, λ₆, λ₇ and λ₈)

Like in FIGS. 1 and 3, the optical transceiver device 700 includes apair of temperature control devices 722, 724 for controlling respectiveregions 712, 714 of the device, as defined by boundaries 702, 704 inFIG. 7, respectively. The operation and positioning of the temperaturecontrol devices 722, 724 has been described in connection with the aboveFIGS. 1-6.

In the example of FIG. 7, the second temperature control device 724 ispositioned to control the temperature of either one of the opticalfilter or the laser, depending on whether the optical device istransmitting or receiving optical signals. In other examples, each ofthe photodetector and the laser may have its own correspondingtemperature control device, such that the device includes a total ofthree temperature control devices. Additionally, each of the filter andlaser may occupy separate regions, and may occupy those respectiveregions with their corresponding temperature control devices.

Additionally or alternatively to the above-described temperature controldevices and routines, in the case of a laser operating on a burst-modetransmission operation, a separate control circuit may be provided forregulating and stabilizing the temperature of the laser. FIG. 8 is ablock diagram of an example system 800 for stabilizing the temperatureof such a laser.

In the example of FIG. 8, a laser 810 receives information in the formof digital signals 815 and transmits the information in the form ofoptical signals 825. The laser 810 may be provided on a chip andincluded in a package (not shown), and may include a heating element 812for regulating a temperature of the laser 810. The heating element 812may be configured to convert an electrical current into heat, such as aresistor is configured to do. Since the laser 810 also generates heatwhen it is in operation, and since the operating wavelength of the laser810 may depend on the temperature of the laser 810, in at least someinstances, the laser 810 and heating element 812 can collectively bethought of as a heating element responsible for regulating the operatingwavelength of the laser.

Transmission operations of the laser 810 are grouped in time-scalepackets of a fixed duration. In a standard time-division multiplexing(TDM) passive optical network (PON) system, this fixed duration iscommonly 125 microseconds. The optical signal is transmitted for only aportion of the fixed duration. The timing of the optical signaltransmission—both in terms of when it begins and how long itlasts—varies from packet to packet. The laser 810 is in an ON stateduring the optical signal transmission, and returns to an OFF state oncethe transmission is complete, even if there is time remaining within thepacket.

The laser is controlled at least in part by a temperature control unit840. The temperature control unit may include a control circuit 842,such as one or more microcontrollers, for receiving input dataindicating a state of the system 800, and a current source 844 or otherpower source for generating a controllable amount of electric current.The current source 844 may be adapted to provide the electric current tothe heating element 812 in order to control a temperature of the laser810. The electric current may be provided via one or more electricalwires. The example of FIG. 8 shows the heating element 812 as part ofthe laser 810 or mounted to the laser packaging. However, in otherexamples, the heating element 812 may be separate from the laser 810,and may even be included in the control unit 840. In yet furtherexamples, both the control unit 840 and heating element 812 may beintegrated with the laser packaging.

The system may further include a burst-mode switch 850 configured toprovide burst-mode switch signaling which is used to control operationof the heating element 812 and the laser 810. The control circuit 842 ofthe temperature control unit 840 receives the signaling from theburst-mode switch 850, and uses the signaling to coordinate operationsof the heating element 812 and laser 810 with one another. In operation,when the control circuit 842 determines an indication of burst modeturning off from the signaling of the burst-mode switch 850, the controlcircuit determines a profile for providing electric current from thecurrent source 844 to the heating element 812, and instructs the currentsource 844 accordingly. Various electric current profiles are shown inthe examples of FIG. 9C, as discussed below in greater detail.

The control circuit 842 also forwards the signaling to the laser 810,but via a time delay circuit 855 having a preset and fixed time delay.The time delay circuit allows for the heating element to respond tosignaling of the burst-mode switch 850 prior to the laser 810 respondingto the same signaling. In this respect, if the signaling instructs thelaser 810 to turn on (e.g., a falling edge of the burst-mode switchsignal), the delay provided by the delay circuit 855 gives the heatingelement 812 sufficient time to warm up the laser 810 before the laser810 is turned on. The time delay is on the order of microseconds, andmay vary depending on the particular application of the system 800.

Other temperature control devices 890, 891 for regional temperatureregulation may be included in the system 800 as previously described inthe present disclosure.

Operation of the burst-mode switch 850, the laser 810, and thetemperature control unit 840 are further shown in FIGS. 9A-9C,respectively. FIG. 9A shows the burst-mode switch 850 alternatingbetween high and low states. FIG. 9B shows the laser 810 switchingbetween high (on) and low (off) states. In the examples of FIGS. 9A and9B: when the burst-mode switch 850 switches from the low state to thehigh state, the laser 810 turns off after a brief time delay; and whenthe burst-mode switch 850 switches from the high state to the low state,the laser 810 turns on after a brief time delay.

FIG. 9C shows electric current outputted by the temperature control unit840. In the example FIG. 9C, the electric current is provided onlyduring the time delay: after the temperature control unit 840 receivesan indication that the burst-mode switch 850 has alternated from thehigh state to the low state; and before the laser 810 turns on.

The amount of current outputted by the temperature control unit 840 isdetermined based on information received from the burst-mode switch.FIGS. 9A-9C show three different examples of operation of the system 800(Examples 1-3) in order to illustrate the factors involved incontrolling the temperature of the laser 810.

In particular, a key factor to temperature control of the laser is theamount of time that the laser is off before turning back on. The amountof time that the laser is off differs in each of Examples 1-3, with thelaser being off the longest amount of time in Example 1 and the shortestamount of time in Example 3. The temperature control unit 840 candetermine how long the laser is off based on the burst-mode switch 850signal. In particular, the time between the burst-mode switch risingedge (switching from low to high) and the burst-mode switch falling edge(switching from high to low) equals the time that the laser is off. Thusthe determination by the temperature control unit is in part ameasurement of how long the laser has been off since the last time thelaser turned off, and also in part a predictive determination of howlong the laser will continue to be off before the laser turns on.

In Example 1, the laser is off for a relatively long time, as indicatedby the long time difference Δ₁ between the rising edge and falling edgeof the burst-mode switch signal. Because the laser has been off for along time, the laser is colder than its normal temperature duringoperation, and if turned on abruptly without first being warmed, couldexhibit a shift in operating wavelength. As a result, during the timedelay, the temperature control unit applies an electric current to theheating element according to a first profile. In Example 1, the firstprofile has a duration of about one quarter of the time delay, and arelatively high magnitude, meaning that a lot of current is delivered tothe heating element over a relatively short time. The first profile isdesigned to increase the temperature of the laser from its very lowtemperature to its normal operating temperature before the laser turnson.

In Example 2, the laser is off for a long time, but not as long of atime as in Example 1. This is indicated by the time difference Δ₂between the rising edge and falling edge of the burst-mode switch signalbeing shorter than the time difference Δ₂ in Example 1. In Example 2,the laser is not as cold as compared to Example 1. Still, timedifference Δ₂ is long enough that if the laser were turned on abruptlywithout first being warmed, it could exhibit an unwanted shift inoperating wavelength. As a result, during the time delay, thetemperature control unit applies an electric current to the heatingelement according to a second profile. The second profile has a durationof about three quarters of the time delay, but a relatively lowmagnitude, meaning that a relatively low current is delivered to theheating element over a relatively long time. The second profile isdesigned to increase the temperature of the laser from its medium-lowtemperature to its normal operating temperature before the laser turnson.

In each of Examples 1 and 2, the temperature control unit cuts off thecurrent supply at or before the time the laser turns on. Continuing toheat the laser after the laser turns on could be counterproductive tomaintaining a stable temperature and operating wavelength, since theheating element could cause the temperature of the laser to increaseabove the laser's normal operating temperature. In addition, not heatingthe laser when the laser is operating may avoid unnecessary operation ofthe heating element for heating, and thus may conserve energy.

Next, in Example 3, the laser is off for a short time. This is indicatedby the short time difference Δ₃ between the rising edge and falling edgeof the burst-mode switch signal. In fact, the time difference Δ₃ inExample 3 is short enough (e.g., less than a predetermined thresholdamount of time) that if the laser does not exhibit an unwanted shift inoperating wavelength when turned on. As a result, there is no need toheat the laser during the time delay, and the temperature control unitapplies no electric current to the heating element.

Particularly, in the case of Example 3, when the control circuit detectsthe falling edge of the burst-mode switch signal, the laser is still ondue to the delayed response time between the previous rising edge of theburst-mode switch signal and the laser. However, even in other caseswhere the laser has already turned off before the control circuitdetects the falling edge of the burst-mode switch signal, the controlcircuit may still determine not to apply an electric current to theheating element if the time difference Δ₃ is short enough.

The above described electric current profiles are presented merely asexamples. Those skilled in the art should understand that other electriccurrent profiles may be provided. For instance, any shape waveform(e.g., sine wave, square wave, sawtooth wave, pulse train, etc.) may beused. The timing of when the wave begins and ends, and the amount of thetime delay for which the wave lasts, may all be varied. Stated anotherway, the example profiles shown in FIGS. 9A-9C are intended merely asexamples and are not intended to in any way limit the type of waveformor profile provided.

Additionally, in each of Examples 1-3 of FIG. 9C, no electrical currentis provided to the heating element before the falling edge of theburst-mode signal. However, those skilled in the art will readilyappreciate that the control circuit can begin controlling the amount andduration of current provided to the heating element after the fallingedge regardless of whether any current is provided before the fallingedge. In this regard, it is possible to provide a small amount ofelectric current to the heater at or after the laser turns off butbefore the burst-mode signal falling edge. In such an instance, thecontrol circuit may determine, upon detecting the falling edge of theburst-mode signal, a change to the amount of current being provided tothe heating element. The change in the current profile may be configuredto sufficiently heat the laser to its operating temperature within theremaining time before the laser turns on, i.e., within the time delay.Therefore, for purposes of the present disclosure, it does not matterhow much current is provided to the heating element before theburst-switch signal turns off, so long as there is a determination of acurrent waveform at or after the falling edge of the burst-mode signal,and so long as the determined current waveform ends at or before thelaser turns on.

The above described operations of FIGS. 9A-9C show a time delay beforeboth the laser turning on and turning off. However, those skilled in theart will readily appreciate that heating a laser before it turns on doesnot require a time delay before the laser turns off. As such, in otherexamples of the present disclosure, the time delay between theburst-mode switch and the laser may be provided only when the laserturns on, and not when the laser turns off. In such cases, the controlcircuit may differentiate between the burst-mode switch turning on oroff, and may only delay operation of the laser in response to theburst-mode switch signaling when the burst-mode signal is determined tohave turned off.

In will also be understood that the above examples of FIGS. 9A-9C applywhen the control circuit has information about both a rising edge andfalling edge on the burst-mode switch signal. However, when an opticaldevice is first turned on, there may not be any burst-mode switch signalrising edge from which to measure an amount of time that the laser hasbeen off. In such cases, an initializing routine may be used instead.Under the initializing routine, the control circuit may instruct thecurrent source to generate electric current even before a falling edgeof the burst-mode switch is detected.

Additionally, in the above examples of FIGS. 9A-9C, the laser is shownas turning on at a falling edge of the burst-mode switch signal, andturning off at a rising edge of the burst-mode switch signal. However,it will be readily appreciated that the laser can alternatively beprogrammed to turn off at the falling edge and on at the rising edge.

Lastly, the example system and routines of FIGS. 8 and 9A-9C aredescribed in connection with a laser. However, those skilled in the artwill appreciate that the same principles may be applied to any opticaldevice for which the operating wavelength of the device changes with thedevice's temperature, and for which operation of the device causes achange in the device's temperature.

As described above, the optical devices, control systems and methods ofthe present disclosure may provide fast and efficient tuning fortransmitting and/or receiving optical signals within a passive opticalnetwork (PON). For instance, these devices, systems and methods may beimplemented in a modem connected to a PON. Furthermore, the devices,systems and methods described herein may be especially advantageous in anext-generation passive optical network (NG-PON), in which data isexpected to be transmitted and received an order of magnitude faster(e.g., ten times faster) than the speed of an ordinary PON.

The above described optical devices, control systems and methods arealso compatible with various aspects described in priority applicationSer. No. 62,507,283. For instance, two feedback mechanisms may beprovided to give feedback regarding the temperature of the laser orother tunable element of the optical device. One feedback mechanism maybe used for coarse tuning (e.g., changing the desired optical signalchannel). Coase tuning of the optical signal may be guided by indirectmeasurements of the signal, such as by measuring a temperature of acomponent of the device (e.g., an optical filter). Another feedbackmechanism may be used to provide fine tuning (e.g., minimizingattenuation of the signal at or around the desired optical signalchannel). Fine tuning of the optical signal may be guided by directmeasurements of the signal, such as by measuring a magnitude of anelectrical current of an electrical signal converted from the opticalsignal. Other aspects of priority application Ser. No. 62,507,283 mayalso be combined with the present disclosure to provide fast, accurateand stable tuning and locking of an optical signal.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. An optical device comprising: at least onetemperature-dependent tunable element for controlling a wavelength of anoptical signal, wherein the tunable element is one of (i) a laser fortransmitting an outgoing optical signal and (ii) an optical filtercoupled to a photodetector for receiving an incoming optical signal; afirst temperature control circuit for controlling a temperature of afirst region of the optical device over a first range of temperaturesbetween a first predetermined temperature and a fourth predeterminedtemperature based on an ambient temperature at the optical device'slocation, wherein at least part of the first range of temperatures isoutside of an operational temperature range of the tunable element; anda second temperature control circuit for controlling a temperature of asecond region of the optical device over a second range of temperaturesbetween a second predetermined temperature and a third predeterminedtemperature based at least in part on a temperature of thetemperature-dependent tunable element, wherein the second regionincludes a portion of the first region, wherein the second region issmaller than the first region, and wherein the tunable element ispositioned in the second region such that a temperature of the tunableelement is controlled based on the second temperature control circuitcontrolling the temperature of the second region, wherein the secondrange of temperatures corresponds to the operational temperature rangeof the tunable element, and wherein the second predetermined temperatureis greater than the first predetermined temperature, the thirdpredetermined temperature is greater than the second predeterminedtemperature, and the fourth predetermined temperature is greater thanthe third predetermined temperature.
 2. The optical device of claim 1,wherein at least one of the first and second temperature controlcircuits is a thermoelectric cooler.
 3. The optical device of claim 1,wherein the second temperature control circuit is configured to controlthe temperature of the tunable element across a range of at least 24° C.4. The optical device of claim 1, wherein the device is an opticaltransceiver comprising each of the laser, the photodetector, and theoptical filter.
 5. The optical device of claim 4, wherein the laser isconfigured to transmit an optical signal at any of at least fourdifferent wavelengths, and wherein the wavelength of the optical signaltransmitted by the laser is based on the temperature of the laser. 6.The optical device of claim 4, wherein the optical transceiver isconfigured to perform one of wavelength-division multiplexing (WDM),dense wavelength-division multiplexing (DWDM), and coarsewavelength-division multiplexing (CWDM).
 7. The optical device of claim1, wherein the second region is defined by a housing, and wherein thesecond temperature control circuit is configured to control thetemperature inside the housing, and wherein the housing is configured toconfine an effect of the second temperature control circuit to thesecond region.
 8. The optical device of claim 1, wherein the firsttemperature control circuit is communicatively coupled to the secondtemperature control circuit and operable to provide an indication of thetemperature of the first region to the second temperature controlcircuit, and wherein the second temperature control circuit isconfigured to control the temperature of the second region based on theindication of the temperature of the first region.
 9. The optical deviceof claim 1, further comprising a control circuit configured to receivean indication of the ambient temperature at the optical device'slocation, and to control the respective temperatures of the first andsecond regions with respect to each other based on the indication of theambient temperature.
 10. The optical device of claim 1, wherein thesecond temperature control circuit is configured to heat the tunableelement, and wherein the wherein the first temperature control circuitmaintains the first region at a temperature lower than the secondtemperature control circuit maintains the second region, whereby whenthe second temperature control circuit is off, the tunable element iscooled, and when the second temperature control circuit is on, thetunable element is heated.
 11. The optical device of claim 1, whereinthe second temperature circuit is configured to adjust the temperatureof the second region at a faster rate than the first temperature circuitis configured to adjust the temperature of the first region.
 12. Theoptical device of claim 1, wherein the first temperature control circuitis configured to create a local heat sinking region in the first region,the heat sinking region having a temperature that is lower than theambient temperature at the optical device's location, and wherein theheat sinking region is configured to accelerate a change to thetemperature of the second region.
 13. The optical device of claim 12,wherein the optical device further comprises a casing, and wherein thelocal heat sinking region is defined by the casing of the device.
 14. Acontrol system included in a device having at least one of (i) a tunableoptical transmitter configured to selectively generate a first opticalsignal at one of a plurality of preselected wavelengths or (ii) anoptical receiver coupled to a tunable optical bandpass filter configuredto selectively pass a second optical signal at one of a plurality ofpreselected wavelengths, wherein the control system is configured to:receive one or more temperature-indicative measurements from a pluralityof corresponding sensors including a first sensor and a second sensor,wherein the first sensor senses an ambient temperature at a location ofthe device, and wherein the second sensor senses a property of thetunable optical transmitter or the tunable optical bandpass filter otherthan temperature that is indicative of a temperature of the tunableoptical transmitter or the tunable optical bandpass filter; transmit afirst control signal to a first temperature control circuit to control atemperature of the device within a first range of temperatures based onthe temperature-indicative measurements received from the first sensor;and transmit a second control signal to a second temperature controlcircuit to control a temperature of the tunable optical transmitter orthe tunable optical bandpass filter within a second range oftemperatures based on one of the temperature-indicative measurementsreceived from the second sensor, wherein the second range oftemperatures is narrower than the first range of temperatures.
 15. Thecontrol system of claim 14, wherein the control system comprises: afirst control circuit coupled to the first sensor, wherein the firstcontrol signal is based on a first temperature measurement of the firsttemperature sensor; and a second control circuit coupled to the secondsensor, wherein the second control signal is based on the propertysensed by the second sensor.
 16. The control system of claim 14, whereinthe control system is configured to provide control signals to both thefirst and second temperature control circuits based on the one or moretemperature-indicative measurements of the first sensor.
 17. The controlsystem of claim 14, wherein the second temperature control circuit isconfigured to receive one or more instruction signals from the firsttemperature control circuit, and wherein the second control signal isbased further on the one or more instruction signals.
 18. The controlsystem of claim 14, wherein the control system is configured to controlthe temperature of the tunable optical transmitter or the tunableoptical bandpass filter across a range of at least 24° C.
 19. Thecontrol system of claim 14, wherein the device includes each of thetunable optical transmitter, the optical receiver, and the opticalbandpass filter coupled to the receiver, and wherein the second controlsignal controls the temperature of the optical transmitter and theoptical bandpass filter and is based on at least one of the receivedtemperature-indicative measurements.
 20. The control system of claim 14,wherein the second range of temperatures is within the first range oftemperatures.
 21. A method for controlling a device having at least oneof (i) a tunable optical transmitter configured to selectively generatea first optical signal at one of a plurality of preselected wavelengthsor (ii) an optical receiver coupled to a tunable optical bandpass filterconfigured to selectively pass a second optical signal at one of aplurality of preselected wavelengths, wherein the method comprises:receiving one or more temperature-indicative measurements from one ormore corresponding sensors including a first sensor and a second sensor,wherein the first sensor senses an ambient temperature at a location ofthe device, and wherein the second sensor senses a property of thetunable optical transmitter or the tunable optical bandpass filter otherthan temperature that is indicative of a temperature of the tunableoptical transmitter or the tunable optical bandpass filter; transmittinga first control signal to a first temperature control circuit to controla temperature of the device within a first range of temperatures basedon the temperature-indicative measurements received from the firstsensor; and transmitting a second control signal to a second temperaturecontrol circuit to control a temperature of the tunable opticaltransmitter or the tunable optical bandpass filter within a second rangeof temperatures based on one of the temperature-indicative measurementsreceived from the second sensor, wherein the second range oftemperatures is narrower than the first range of temperatures.